ConcurrentHashMap

Creates a new, empty map with the default initial table size (16).

Creates a new, empty map with an initial table size accommodating the specified number of elements without the need to dynamically resize.

Creates a new map with the same mappings as the given map.

Creates a new, empty map with an initial table size based on the given number of elements ( initialCapacity ) and initial table density ( loadFactor ).

Creates a new, empty map with an initial table size based on the given number of elements ( initialCapacity ), table density ( loadFactor ), and number of concurrently updating threads ( concurrencyLevel ).

Removes all of the mappings from this map.

Legacy method testing if some key maps into the specified value in this table. This method is identical in functionality to containsValue(Object) , and exists solely to ensure full compatibility with class Hashtable .

Tests if the specified object is a key in this table.

Returns true if this map maps one or more keys to the specified value. Note: This method may require a full traversal of the map, and is much slower than method containsKey .

Returns an enumeration of the values in this table.

Returns a Set view of the mappings contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from the map, via the Iterator.remove , Set.remove , removeAll , retainAll , and clear operations.

The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException , and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Compares the specified object with this map for equality. Returns true if the given object is a map with the same mappings as this map. This operation may return misleading results if either map is concurrently modified during execution of this method.

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key k to a value v such that key.equals(k) , then this method returns v ; otherwise it returns null . (There can be at most one such mapping.)

Returns the hash code value for this Map , i.e., the sum of, for each key-value pair in the map, key.hashCode() ^ value.hashCode() .

Returns whether this map is empty.

This implementation compares size() to 0.

Returns a Set view of the keys contained in this map. The set is backed by the map, so changes to the map are reflected in the set, and vice-versa. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove , Set.remove , removeAll , retainAll , and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException , and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.

Returns an enumeration of the keys in this table.

Maps the specified key to the specified value in this table. Neither the key nor the value can be null.

The value can be retrieved by calling the get method with a key that is equal to the original key.

Copies all of the mappings from the specified map to this one. These mappings replace any mappings that this map had for any of the keys currently in the specified map.

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to

          
           if (!map.containsKey(key))
   return map.put(key, value);
 else
   return map.get(key);
          
         

Removes the entry for a key only if currently mapped to a given value. This is equivalent to

          
           if (map.containsKey(key) && map.get(key).equals(value)) {
   map.remove(key);
   return true;
          
          else
   return false;}
         

Removes the key (and its corresponding value) from this map. This method does nothing if the key is not in the map.

Replaces the entry for a key only if currently mapped to some value. This is equivalent to

          
           if (map.containsKey(key)) {
   return map.put(key, value);
          
          else
   return null;}
         

Replaces the entry for a key only if currently mapped to a given value. This is equivalent to

          
           if (map.containsKey(key) && map.get(key).equals(oldValue)) {
   map.put(key, newValue);
   return true;
          
          else
   return false;}
         

Returns the number of mappings in this Map .

This implementation returns its entry set's size.

Returns a string representation of this map. The string representation consists of a list of key-value mappings (in no particular order) enclosed in braces (" { }"). Adjacent mappings are separated by the characters ", " (comma and space). Each key-value mapping is rendered as the key followed by an equals sign (" = ") followed by the associated value.

Returns a Collection view of the values contained in this map. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove , Collection.remove , removeAll , retainAll , and clear operations. It does not support the add or addAll operations.

The view's iterator is a "weakly consistent" iterator that will never throw ConcurrentModificationException , and guarantees to traverse elements as they existed upon construction of the iterator, and may (but is not guaranteed to) reflect any modifications subsequent to construction.